How can I show product reviews on the recommendations widget
To show the product reviews, you'll have to access the 'App preferences page' (How can I access the app preferences page?).
After you have accessed it, you need to select the Visual preferences option and on it, click on the Rating section (or the score stars on the image):
Here, you will be able to configure the app with the review app you are using in order to display the product ratings, as well as modifying multiple visual aspects of it.